The use of invasive medical devices, such as catheters and laparoscopes in order to gain access into interior regions or spaces of the body for performing diagnostic and therapeutic procedures is well known. In such procedures, it is important for a physician or technician to be able to precisely position the device, including various functional elements located on the device, within the body in order to make contact with a desired body tissue location.
For example, the need for precise control over the positioning of an invasive catheter or surgical probe is especially critical during procedures for testing or ablating myocardial tissue within the beating heart for treating cardiac rhythm disturbances. To perform such a procedure, the physician typically steers a catheter through a main vein or artery into the interior region of the heart that is to be treated. The physician then manipulates the catheter in order to place one or more electrodes carried on the distal portion and/or tip of the catheter into direct contact with the endocardial tissue. The physician may use the electrode(s) to examine the propagation of electrical impulses in heart tissue in order to locate aberrant conductive pathways and to identify the arrhythmia foci. This procedure is called mapping. One such mapping technique is to introduce multiple-electrode array structures carried on the distal end of an invasive catheter into the heart through venous or arterial access. Information obtained from the various electrode elements (operating in either unipolar or bipolar fashion), combined with externally obtained electrocardiogram signals, can be externally processed to detect local electrical events and identify likely arrhythmia foci locations within the heart.
Using the same, or a different catheter or surgical probe device, the physician may then direct energy from one or more distally carried electrode(s) through the myocardial tissue either to an indifferent electrode (in a unipolar electrode arrangement) or to an adjacent electrode (in a bipolar electrode arrangement) to ablate the tissue locations containing the aberrant conductive pathways in order to restore a healthy heart rhythm. This procedure is called ablation therapy.
In theory, minimally invasive mapping techniques allow a physician to identify a target ablation site within the heart, prior to the actual ablation procedure and without the complications of open heart surgery. In practice, however, current minimally invasive mapping techniques do not ensure that an identified target site will be accurately or easily relocated. Accordingly, it would be desirable to provide physicians with the ability to accurately return to a target site in the heart that was previously identified using minimally invasive mapping techniques.
One proposed solution to the problem of identifying and relocating target sites in the heart site is to add a navigation system that is centered outside of a patient's body, in order to provide an “absolute” reference frame that is unaffected by the absolute location of the patient. One such system, disclosed in U.S. Pat. No. 5,391,199 to Ben-Haim (“the '199 patent”), combines an electrophysiological mapping system and a navigational system centered on a reference frame outside of the body in order to attempt to increase a physician's ability to return to an identified target site. The mapping system provides data on points of interest at sites within the body. The exterior navigational system provides data on the “absolute” location of the site with respect to an external reference frame of the site as these points of interest are identified. This is accomplished by placing one or more location sensors adjacent mapping elements on the mapping probe. As taught in the '199 patent, combining the “location information” with “local information” for a sufficient number of sites will provide a three dimensional “map” of data points corresponding to the three-dimensional structure of the heart or other organ.
One problem, however, occurs with mapping catheters having relatively small mapping element carrying structures, e.g., 3-D catheter structures that are 40 mm in diameter or smaller. In these cases, it is difficult to place location elements adjacent all of the mapping elements, and sometimes even adjacent a select few of the mapping elements. Thus, generating a three dimensional map is made difficult. Another problem occurs as a result of the discrete nature of the mapping elements. Oftentimes, critical information is missed between the mapping elements, resulting in a map that, although corresponding to the three-dimensional structure of the heart or other organ, does not accurately identify target sites.